Azafluorene derivative and organic light-emitting device using the derivative

ABSTRACT

A novel azafluorene derivative and an organic light-emitting device having the derivative are provided. The organic light-emitting device includes a pair of electrodes composed of an anode and a cathode one of which is a transparent or semi-transparent electrode, and an organic compound layer interposed between the pair of electrodes. The organic compound layer contains the azafluorene derivative represented by the following general formula (I):

The present application is a divisional of U.S. patent application Ser.No. 11/961,801 filed Dec. 20, 2007, the entire disclosure of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel azafluorene derivative and anorganic light-emitting device using the derivative.

2. Description of the Related Art

An organic light-emitting device is a device having a thin film whichcontains a fluorescent or phosphorescent organic compound and isinterposed between electrodes. Electrons and holes are injected from therespective electrodes, whereby excitons of the fluorescent orphosphorescent compound are produced. The excitons emit light when theyreturn to their ground states.

The development of an organic light-emitting device is remarkable, andthe characteristics of the device are such that luminance is high at lowapplied voltage, lights with various wavelengths can be emitted, thespeed of response is high, its thickness is thin and its weight islight. Accordingly, the device has potential for a variety ofapplications.

However, the present situation calls for optical output with higherluminance or higher conversion efficiency. In addition, many problemsstill remain unsolved regarding durability against changes over time dueto long-term use, and deterioration caused by atmospheric gas containingoxygen or moisture. Further, when considering application to a fullcolor display, the present art is still insufficient to address problemsconcerning need for light emission of blue, green, and red with highcolor purity.

In the organic light-emitting device, an electron transport layer incontact with a light-emitting layer on the cathode side, an electroninjection layer and a hole-blocking layer are not directly involved inthe light emission of the device. However, each of the layers largelyaffects the light-emitting characteristic and durability of the devicefrom the viewpoint of, for example, a carrier balance in thelight-emitting layer. In general, heterocyclic derivatives are oftenused in the electron transport layer.

Azafluorene derivatives are included in the heterocyclic derivatives,and the case where an azafluorene derivative is used in an organiclight-emitting device is described in, for example, each of JapanesePatent Application Laid-Open No. 2005-314663, WO 2006/081973, and Org.Lett., 8, 1415 (2006). In each of Japanese Patent Application Laid-OpenNo. 2005-314663 and WO 2006/081973, an azafluorene derivative is used asa ligand of a metal complex in an organic light-emitting device. Org.Lett., 8, 1415 (2006) proposes that an azafluorene derivative whoseazafluorene ring is substituted by an aryl group at the 9-position isused in an organic light-emitting device. However, there is no report onan example in which an azafluorene derivative obtained by substituting9-position of an azafluorene ring by an alkyl group is used by itselfand not as a ligand of a metal complex in an organic light-emittingdevice, in particular, in an electron transport layer.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel azafluorenederivative. The compound can be used as, for example, a material for anorganic light-emitting device. In addition, another object of thepresent invention is to provide an organic light-emitting device whichuses the material for an organic light-emitting device and has goodemission efficiency and high durability. Further, still another objectof the present invention is to provide an organic light-emitting devicethat can be easily produced at a relatively low cost.

The inventors of the present invention have made extensive studies withthe view to solving the above-mentioned problems.

As a result, the inventors have completed the present invention.

The present invention provides an azafluorene derivative represented bythe following general formula (I):

where: n and m each independently represent an integer of 1 to 4, arepresents an integer of 0 to 4, and b represents an integer of 0 to 3;one of Z₁ to Z₈ represents a nitrogen atom, and the other seven eachrepresent a carbon atom; Y₁ represents a substituent selected from thegroup consisting of a hydrogen atom, a substituted or unsubstitutedaromatic hydrocarbon group, and a substituted or unsubstitutedheterocyclic group; Y₂ represents a single bond, a divalent aromatichydrocarbon group which may be substituted, or a divalent heterocyclicgroup which may be substituted; X₁ and X₂ each independently represent asubstituent selected from the group consisting of a substituted orunsubstituted alkyl group, a substituted or unsubstituted alkoxy group,a substituted or unsubstituted aromatic hydrocarbon group, a substitutedor unsubstituted heterocyclic group, and a substituted amino group; Arrepresents an m-valent aromatic hydrocarbon group which may besubstituted or an co-valent heterocyclic group which may be substituted,provided that Ar may represent a hydrogen atom when m represents 1; R₁and R₂ each independently represent an alkyl group which isunsubstituted or may be substituted by a fluorine atom; when arepresents 2 or more, X₁'s may be identical to or different from eachother; when b represents 2 or more, X₂'s may be identical to ordifferent from each other; when n represents 2 or more, the types ofcoupled azafluorene units may be identical to or different from eachother; and when m represents 2 or more, Y₁'s or Y₂'s may be identical toor different from each other, and the number and types of azafluoreneunits coupled with Ar through Y₂ may be identical to or different fromeach other.

The novel azafluorene derivative of the present invention has highchemical stability, and is excellent in electron transport performance.Accordingly, the derivative can be used as a material for an organiclight-emitting device. In particular, an organic light-emitting deviceusing the novel azafluorene derivative in its electron transport layercan be driven at low voltage, has good emission efficiency, and has highdurability in long-term driving. In addition, an organic light-emittingdevice of the present invention can be produced by employing, forexample, a vacuum deposition method or a casting method, and alarge-area device can be easily produced at a relatively low cost.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the first embodiment of the organiclight-emitting device of the present invention.

FIG. 2 is a sectional view showing the second embodiment of the organiclight-emitting device of the present invention.

FIG. 3 is a sectional view showing the third embodiment of the organiclight-emitting device of the present invention.

FIG. 4 is a view showing the ¹H-NMR spectrum (solvent: CDCl₃) ofExemplified Compound 215.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the present invention will be described in detail.

First, an azafluorene derivative of the present invention will bedescribed. The azafluorene derivative of the present invention as amaterial for an organic light-emitting device will be described.

The material for an organic light-emitting device of the presentinvention is an azafluorene derivative represented by the followinggeneral formula (I).

In the formula (I), one of Z₁ to Z₈ represents a nitrogen atom, and theother seven each represent a carbon atom.

In the formula (I), Y₁ represents a substituent selected from the groupconsisting of a hydrogen atom, a substituted or unsubstituted aromatichydrocarbon group, and a substituted or unsubstituted heterocyclicgroup.

Examples of the aromatic hydrocarbon group represented by Y₁ include,but are not limited to, a phenyl group, a naphthyl group, an azulenylgroup, an indenyl group, an anthracenyl group, a phenanthryl group, apyrenyl group, a chrysenyl group, a dibenzochrysenyl group, abenzoanthracenyl group, dibenzoanthracenyl group, a naphthacenyl group,a picenyl group, a pentacenyl group, a fluorenyl group, a biphenylenylgroup, a triphenylenyl group, a fluoranthenyl group, abenzofluoranthenyl group, and a perylenyl group.

Examples of the heterocyclic group represented by Y₁ include, but arenot limited to, a pyridyl group, a pyridazyl group, a pyrimidinyl group,a pyrazinyl group, a triazinyl group, a quinolyl group, an isoquinolylgroup, a phthalazinyl group, a quinazolinyl group, a quinoxalinyl group,a naphthylidinyl group, an acridinyl group, a phenanthrolyl group, adiazafluorenyl group, phenadinyl group, a pyrrolyl group, a pyrazolylgroup, an imidazolyl group, a triazolyl group, an indolyl group, anindolizinyl group, a benzoimidazolyl group, a carbazolyl group, abenzocarbazolyl group, a thienyl group, a benzothienyl group, adibenzothienyl group, a furyl group, a benzofuryl group, anisobenzofuryl group, a dibenzofuryl group, an oxazolyl group, anisoxazolyl group, a benzoxazolyl group, an oxadiazolyl group, athiazolyl group, an isothiazolyl group, a benzothiazolyl group, and athiadiazolyl group.

Examples of substituents with which the aromatic hydrocarbon group andthe heterocyclic group may be substituted include, but are not limitedto, alkyl groups such as a methyl group, an ethyl group, and atert-butyl group; aromatic hydrocarbon groups such as a phenyl group, anaphthyl group, a fluorenyl group, and a phenanthryl group; heterocyclicgroups such as a thienyl group, a pyrrolyl group, a pyridyl group, and aquinolyl group; substituted amino groups such as a dimethylamino group,a diethylamino group, a dibenzylamino group, and a diphenylamino group;alkoxy groups such as a methoxy group and an ethoxy group; halogen atomssuch as fluorine, chlorine, bromine, and iodine; hydroxyl groups; cyanogroups; and nitro groups.

In the formula (I), Y₂ represents a single bond, a divalent aromatichydrocarbon group which may be substituted, or a divalent heterocyclicgroup which may be substituted.

Examples of the aromatic hydrocarbon group represented by Y₂ include,but are not limited to, a benzene-1,2-diyl group, a benzene-1,3-diylgroup, a benzene-1,4-diyl group, a napthalene-1,4-diyl group, anaphthalene-2,7-diyl group, a phenanthrene-2,7-diyl group, afluorene-2,7-diyl group, a fluorene-3,6-diyl group, ananthracene-2,6-diyl group, an anthracene-9,10-diyl group, and apyrene-1,3-diyl group.

Examples of the heterocyclic group represented by Y₂ include, but arenot limited to a pyridine-2,4-diyl group, a pyridine-2,6-diyl group, aquinoline-2,4-diyl group, a [1,8]naphthylidine-2,7-diyl group, a[1,8]naphthylidine-3,6-diyl group, a [4,5]diazafluorene-2,7-diyl group,a [1,10]phenanthroline-2,9-diyl group, and a 1,3,4-oxadiazole-2,5-diylgroup.

Examples of substituents with which the divalent aromatic hydrocarbongroup and the divalent heterocyclic group may be substituted include,but are not limited to, alkyl groups such as a methyl group, an ethylgroup, and a tert-butyl group; aromatic hydrocarbon groups such as aphenyl group, a naphthyl group, a fluorenyl group, and a phenanthrylgroup; heterocyclic groups such as a thienyl group, a pyrrolyl group, apyridyl group, and a quinolyl group; substituted amino groups such as adimethylamino group, a diethylamino group, a dibenzylamino group, and adiphenylamino group; alkoxy groups such as a methoxy group and an ethoxygroup; halogen atoms such as fluorine, chlorine, bromine, and iodine;hydroxyl groups; cyano groups; and nitro groups.

In the formula (I), X₁ and X₂ each independently represent a substituentselected from the group consisting of a substituted or unsubstitutedalkyl group, a substituted or unsubstituted alkoxy group, a substitutedor unsubstituted aromatic hydrocarbon group, a substituted orunsubstituted heterocyclic group, and a substituted amino group.

Examples of the alkyl groups represented by X₁ and X₂ include, but arenot limited to, a methyl group, an ethyl group, an n-propyl group, ann-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group,an n-octyl group, an n-decyl group, an iso-propyl group, aniso-propyl-d7 group, an iso-butyl group, a sec-butyl group, a tert-butylgroup, a tert-butyl-d9 group, an iso-pentyl group, a neopentyl group, atert-octyl group, a cyclopropyl group, a cyclobutyl group, a cyclopentylgroup, a cyclohexyl group, a norbornyl group, and an adamantyl group.

Examples of the alkoxy groups represented by X₁ and X₂ include, but arenot limited to, alkyloxy groups having the above alkyl groups such as amethoxy group, an ethoxy group, a n-propoxy group, an iso-propoxy group,a n-butoxy group, a tert-butoxy group, and a cyclohexyloxy group.

Examples of the aromatic hydrocarbon groups represented by X₁ and X₂include, but are not limited to, a phenyl group, a naphthyl group, anazulenyl group, an indenyl group, an anthracenyl group, a phenanthrylgroup, a pyrenyl group, a chrysenyl group, a dibenzochrysenyl group, abenzoanthracenyl group, a dibenzoanthracenyl group, a naphthacenylgroup, a picenyl group, a pentacenyl group, a fluorenyl group, abiphenylenyl group, a triphenylenyl group, a fluoranthenyl group, abenzofluoranthenyl group, and a perylenyl group.

Examples of the heterocyclic groups represented by X₁ and X₂ include,but are not limited to, a pyridyl group, a pyridazyl group, apyrimidinyl group, a pyrazinyl group, a triazinyl group, a quinolylgroup, an isoquinolyl group, a phthalazinyl group, a quinazolinyl group,a quinoxalinyl group, a naphthylidinyl group, an acridinyl group, aphenanthrolyl group, a diazafluorenyl group, phenadinyl group, apyrrolyl group, a pyrazolyl group, an imidazolyl group, a triazolylgroup, an indolyl group, an indolizinyl group, a benzoimidazolyl group,a carbazolyl group, a benzocarbazolyl group, a thienyl group, abenzothienyl group, a dibenzothienyl group, a furyl group, a benzofurylgroup, an isobenzofuryl group, a dibenzofuryl group, an oxazolyl group,an isoxazolyl group, a benzoxazolyl group, an oxadiazolyl group, athiazolyl group, an isothiazolyl group, a benzothiazolyl group, and athiadiazolyl group.

Examples of the substituted amino groups represented by X₁ and X₂include, but are not limited to, a dimethylamino group, a diethylaminogroup, a dibenzylamino group, a diphenylamino group, a ditolylaminogroup, a dianisolylamino group, a fluorenylphenylamino group, adifluorenylamino group, a naphthylphenylamino group, and adinaphthylamino group.

Examples of substituents with which the alkyl group, the alkoxy group,the aromatic hydrocarbon group and the heterocyclic group may besubstituted include, but are not limited to, alkyl groups such as amethyl group, an ethyl group, and a tert-butyl group; aromatichydrocarbon groups such as a phenyl group, a naphthyl group, a fluorenylgroup, and a phenanthryl group; heterocyclic groups such as a thienylgroup, a pyrrolyl group, a pyridyl group, and a quinolyl group; aminogroups such as a dimethylamino group, a diethylamine group, adibenzylamino group, and a diphenylamino group; alkoxy groups such as amethoxy group and an ethoxy group; halogen atoms such as fluorine,chlorine, bromine, and iodine; hydroxyl groups; cyano groups; and nitrogroups.

In the formula (I), Ar represents an m-valent aromatic hydrocarbon groupwhich may be substituted or an m-valent heterocyclic group which may besubstituted.

The m-valent aromatic hydrocarbon group is constituted of an aromatichydrocarbon ring or an aromatic hydrocarbon ring. Examples of thearomatic hydrocarbon ring or aromatic hydrocarbon ring include, but arenot limited to, benzene, naphthalene, azulene, indene, anthracene,phenanthrene, pyrene, chrysene, dibenzochrysene, benzoanthracene,dibenzoanthracene, naphthacene, picene, pentacene, fluorene,biphenylene, triphenylene, fluoranthene, benzofluoranthene, perylene,biphenyl, o-terphenyl, m-terphenyl, p-terphenyl, binaphthyl,phenylnaphthalene, and phenylfluorene.

The m-valent heterocyclic group is constituted of a heterocyclic ring ora heterocyclic ring. Examples of the heterocyclic ring or heterocyclicring include, but are not limited to, pyridine, pyridazine, pyrimidine,pyradine, triazine, quinoline, isoquinoline, phthalazine, quinazoline,quinoxaline, naphthyridine, acridine, phenanthroline, diazafluorene,phenazine, pyrrole, pyrazole, imidazole, triazole, indole, indolizine,benzoimidazole, carbazole, benzocarbazole, thiophene, benzothiophene,dibenzothiophene, furan, benzofuran, dibenzofuran, oxazole, benzoxazole,oxadiazole, thiazole, benzothiazole, thiadiazole, dihydrophenanthroline,phenanthridine, bipyridine, and dioxazolobenzene.

Ar may represent a hydrogen atom when m represents 1.

In the formula (I), R₁ and R₂ each independently represent an alkylgroup which is unsubstituted or may be substituted by a fluorine atom.

Examples of the alkyl groups represented by R₁ and R₂ include, but arenot limited to, a methyl group, an ethyl group, an n-propyl group, ann-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group,an n-octyl group, an n-decyl group, an iso-propyl group, aniso-propyl-d7 group, an iso-butyl group, a sec-butyl group, a tert-butylgroup, a tert-butyl-d9 group, an iso-pentyl group, a neopentyl group, atert-octyl group, a cyclopropyl group, a cyclobutyl group, a cyclopentylgroup, a cyclohexyl group, a norbornyl group, and an adamantyl group.

In addition, a hydrogen atom in the azafluorene derivative representedby the formula (I) may be replaced with a deuterium atom.

In the formula (I), n represents an integer of 1 to 4, and representsthe number of coupled azafluorene units.

In the formula (I), m represents an integer of 1 to 4, and representsthe number of azafluorene units or the groups of the units bonded to Arthrough Y₂.

In the formula (I), a represents an integer of 0 to 4.

In the formula (I), b represents an integer of 0 to 3.

When a represents 2 or more, X₁'s may be identical to or different fromeach other. In addition, when b represents 2 or more, X₂'s may beidentical to or different from each other. When n represents 2 or more,coupled azafluorene units may be identical to or different from eachother. When m represents 2 or more, Y₁'s or Y₂'s may be identical to ordifferent from each other, and the numbers or types of azafluorene unitscoupled with Ar through Y₂ may be identical to or different from eachother.

The azafluorene derivative represented by the formula (I) is preferablya compound represented by the following general formula (II).

In the formula (II), one of Z₄ and Z₅ represents a nitrogen atom, andthe other represents a carbon atom.

In the formula (II), m, a, b, X_(I), X₂, Ar, R₁, and R₂ each have thesame meaning as defined in the general formula (I).

The azafluorene derivative represented by the formula (I) is morepreferably a compound represented by the following general formula(III).

In the formula (III), m, a, b, X₁, X₂, Ar, R₁, and R₂ each have the samemeaning as defined in the general formula (I).

The azafluorene derivative represented by the formula (I) is morepreferably a compound represented by the following general formula (IV).

In the formula (IV), a, b, X₁, X₂, Ar, R₁, and R₂ each have the samemeaning as defined in the general formula (I).

A suitable example of the azafluorene derivative represented by theformula (I) is a compound represented by the following general formula(V).

In the formula (V), one of Z₄ and represents a nitrogen atom, and theother represents a carbon atom.

In the formula (V), Y₃ represents a group selected from the groupconsisting of a hydrogen atom, a substituted or unsubstituted aromatichydrocarbon group, and a substituted or unsubstituted heterocyclicgroup.

Examples of the aromatic hydrocarbon group represented by Y₃ include thesame substituents as those represented by Y₁ of the general formula (I).

Examples of the heterocyclic group represented by Y₃ include the samesubstituents as those represented by Y₁ of the general formula (I).

Examples of the substituents with which the above aromatic hydrocarbongroup and the above heterocyclic group may be substituted include thesame substituents as those with which Y₁ of the general formula (I) maybe substituted.

In the formula (V), n, a, b, Y₁, X₁, X₂, Ar, R₁, and R₂ each have thesame meaning as defined in the general formula (I).

The material for the organic light-emitting device of the presentinvention can be preferably used as an electron transport material. Whenusing the material for the organic light-emitting device of the presentinvention as an electron transport material, the light-emittingcharacteristic of the organic light-emitting device can be improved.

With regard to an improvement in light-emitting characteristics of anorganic light-emitting device, when using as an electron transportmaterial in an electron transport layer a material which is excellent inelectron transport property and facilitates injection of electrons intoa light-emitting layer, it is expected that a voltage at which thedevice is driven is reduced, the emission efficiency of the deviceincreases, and the lifetime of the device is elongated. In such a case,electrons can be efficiently injected into the light-emitting layer at alow driving voltage, and an environment in which material degradationsuch as carrier accumulation may be promoted can be eliminated.

In order to enhance electron transport performance, it is consideredthat it is useful to introduce a heteroaromatic ring which has a widen-conjugated system and is capable of enlarging the extent to which itsn-conjugated plane overlaps with that of an adjacent molecule. In thepresent invention, a compound having an azafluorene ring is introducedas an electron transport material. The azafluorene ring has not only alarge n-conjugated system but also a planar structure not present inphenylpyridine that has been conventionally used. Accordingly, themolecular orbital of the azafluorene derivative overlaps with that of anadjacent molecule to a large extent, and the derivative is expected tohave excellent electron transport performance. Further, the azafluorenering has a band gap larger than a phenanthroline ring or a quinolinering by virtue of distortion caused by its central five-membered ring.Therefore, the HOMO level of the azafluorene derivative is lower thanthat of a phenanthroline derivative or a quinoline derivative as long asthe LUMO level of the azafluorene derivative is maintained at the samelevel as that of the phenanthroline derivative or the quinolinederivative. Since a material having a low HOMO level exhibits highhole-blocking properties, when using the azafluorene derivative in theelectron transport layer, carriers can be inhibited from leaking out ofthe light-emitting layer, and light emission with high efficiency can beexpected.

However, in an azafluorene compound whose which azafluorene ring is notsubstituted at the 9-position, a carbon atom having high reactionactivity is present at the 9-position, and the carbon atom has activehydrogen. Therefore, when the azafluorene compound whose azafluorenering is not substituted at the 9-position is used in the electrontransport layer, radical anions produced during the course oftransporting electrons may be chemically unstable. In addition, theinstability may cause material degradation such as heat decomposition atthe time of driving the device to remarkably degrade the light-emittingcharacteristic of the device.

With the aim of solving this problem, a substituent need be introducedto the azafluorene ring at the 9-position. In this case, an aryl groupis often introduced at the 9-position because a target compound can besynthesized by a simple method. However, a quaternary carbon atom towhich four aryl groups are bonded is present even in a9,9-diaryl-substituted azafluorene compound having aryl groupsintroduced at the 9-position, and hence, a tertiary carbon radical isapt to be produced by heat decomposition. Accordingly, the heatstability of the compound itself is reduced. Therefore, even when anazafluorene compound whose azafluorene ring is substituted with an arylgroup is used in an electron transport layer, the light-emittingcharacteristic of an organic light-emitting device may deteriorate as inthe case of an azafluorene compound whose azafluorene ring is notsubstituted at the 9-position.

In view of the foregoing, the azafluorene ring of the azafluorenederivative used as the material for the organic light-emitting device ofthe present invention is substituted by an alkyl group at the9-position. Thus, the compound itself has a chemically and thermallystable structure, and can be inhibited from undergoing materialdegradation due to heat decomposition when being used in an organiclight-emitting device.

As described above, the material for the organic light-emitting deviceof the present invention can exert electron injection/transportproperties and hole-blocking properties intrinsic to the above-mentionedazafluorene derivative in an organic light-emitting device and improvethe light-emitting characteristic of the organic light-emitting device.

The specific structural formulae of the azafluorene derivative as thematerial for the organic light-emitting device of the present inventionare shown below. However, the azafluorene derivative of the presentinvention is by no means limited to the following structural formulae.

Next, the organic light-emitting device of the present invention will bedescribed in detail.

The organic light-emitting device of the present invention includes apair of electrodes composed of an anode and a cathode and at least onelayer interposed between the pair of electrodes, containing an organiccompound, either the anode or the cathode being transparent orsemi-transparent electrode. In addition, the organic light-emittingdevice of the present invention contains at least one type of materialfor the organic light-emitting device of the present invention in thelayer containing an organic compound. The organic light-emitting deviceof the present invention is preferably an electroluminescence devicethat emits light by applying a voltage between a pair of electrodes.

Hereinafter, the organic light-emitting device of the present inventionwill be described in detail with reference to the drawings.

FIG. 1 is a sectional view illustrating the first embodiment of theorganic light-emitting device according to the present invention. Theorganic light-emitting device 10 in FIG. 1 includes an anode 2, anorganic light-emitting layer 3 and a cathode 4, which are sequentiallyformed on a substrate 1. The organic light-emitting device 10 is usefulin a case where the light-emitting layer 3 is formed form a compoundwhich has all the properties including a hole transporting ability, anelectron transporting ability and a light emitting property or a casewhere the light-emitting layer 3 is formed from a mixture of compoundseach having one of a hole transporting ability, an electron transportingability and a light emitting property.

FIG. 2 is a sectional view illustrating the second embodiment of theorganic light-emitting device according to the present invention. Anorganic light-emitting device 20 of FIG. 2 includes an anode 2, a holetransport layer 5, an electron transport layer 6 and a cathode 4, whichare sequentially formed on a substrate 1. The organic light-emittingdevice 20 is useful in a case where a light emitting compound having ahole transporting property and/or electron transporting property and anorganic compound having only an electron transporting property or only ahole transporting property are used in combination. In addition, in thelight-emitting layer 20, the hole transport layer 5 or the electrontransport layer 6 serves as the light-emitting layer.

FIG. 3 is a sectional view illustrating the third embodiment of theorganic light-emitting device according to the present invention. Anorganic light-emitting device 30 of FIG. 3 illustrate a structure inwhich the light-emitting layer 3 is inserted between a hole transportlayer 5 and an electron transport layer 6 in the organic light-emittingdevice 30 of FIG. 2. In the organic light-emitting device 30, acarrier-transporting function and a light-emitting function areseparated from each other. Thus, the device can be used appropriately incombination with compounds each having one of a hole-transportingproperty, electron transporting property and light emitting property.Therefore, the degree of freedom of material selection extremelyincreases, and additionally, since various compounds different from eachother in emission wavelength can be used, luminescent hues can bediversified. Further, the emission efficiency of the organiclight-emitting device 30 can be improved by effectively trappingcarriers or excitons in the light-emitting layer 3.

Further, in FIG. 3, a hole injection layer may be inserted between theanode 2 and the hole transport layer 5. The insertion of the holeinjection layer in the organic light-emitting device improves theadhesiveness between the anode 2 and the hole transport layer 5, or thehole injection property, and hence, is effective in reducing voltage atwhich the device is driven.

Further, in FIG. 3, a layer for inhibiting holes or excitons escapingthrough the side of the cathode 4 (hole blocking layer/exciton blockinglayer) may be inserted between the light-emitting layer 3 and theelectron transport layer 6. A compound having high ionization potentialis used as the hole blocking layer/exciton blocking layer to improve theemission efficiency of the organic light-emitting device.

It should be noted that FIGS. 1 to 3 merely illustrate very basic devicestructures, and the structure of the organic light-emitting device ofthe present invention is not limited thereto. For example, it ispossible to adopt various layer structures as follows: an insulatinglayer, an adhesive layer or an interference layer is provided to theinterface between an electrode and an organic layer; and a holetransport layer is composed of two layers different in ionizationpotential.

At least one type of material for the organic light-emitting device ofthe present invention is contained in a layer formed from an organiccompound such as the light-emitting layer 3, the hole transport layer 5,or the electron transport layer 6 shown in FIGS. 1 to 3. The material isincorporated into preferably the hole-blocking layer, the electrontransport layer or an electron injection layer, or particularlypreferably the electron transport layer.

In general, when a layer having an electron transport property isprovided between the light-emitting layer and cathode of an organiclight-emitting device, the following four functions are primarilyrequired for the layer having an electron transport property. The layeris referred to as an electron injection layer, an electron transportlayer, an exciton-blocking layer or a hole-blocking layer for eachfunction.

(1) Receiving electrons injected from the cathode (electron injection).

(2) Transporting electrons to the light-emitting layer (electrontransport).

(3) Blocking the escape of excitons from the light-emitting layer(exciton block)

(4) Blocking the leakage of holes from the light-emitting layer (holeblock)

An electron transport layer formed from a single electron transportmaterial may be provided with those functions. Alternatively, alaminated structure may be composed of multiple layers formed frommaterials different in function such as an electron transport layer andan electron injection layer.

It is known that a heteroaromatic ring derivative typified by anoxadiazole derivative, a quinoline derivative or a phenanthrolinederivative is generally preferable as an electron transport material interms of the above-mentioned functions of the electron transport layer.However, an organic light-emitting device using any one of such electrontransport materials in its electron transport layer still involves alarge number of problems concerning the voltage at which the device isdriven, emission efficiency and durability. Therefore, when using theazaphenanthrene derivative of the present invention, these problems canbe solved.

In an organic layer containing the material for the organiclight-emitting device of the present invention, the material for theorganic light-emitting device may be used alone, or may be mixed withany other material to form a mixed organic layer. When being used forthe mixed organic layer, the content of the material for the organiclight-emitting device of the present invention is 0.01 wt % or more and99.99 wt % or less and preferably 5 wt % or more and 95 wt % or less.Similarly, the material for the organic light-emitting device of thepresent invention may be mixed with any other inorganic compound to forma mixed layer. For example, it is possible that the azafluorenederivative as the material for the organic light-emitting device of thepresent invention is doped with an alkali metal to form an electroninjection layer between an electron transport layer and a cathode.

In the organic light-emitting device of the present invention, a holetransport (injection) layer, a light-emitting layer, an electrontransport (injection) layer, etc. can be provided by usingconventionally known low- and high-molecular-weight-type materials foran organic light-emitting device together with the material for theorganic light-emitting device of the present invention as required.

A material in which holes are easily injected from the anode and whichhas high hole mobility with which the injected hole is transported tothe light-emitting layer is preferably used in the hole transport(injection) layer. Examples of such a hole injection/transport materialincludes, but is not limited to, a triarylamine derivative, aphenylenediamine derivative, a stilbene derivative, a phthalocyaninederivative, a porphyrin derivative, poly(vinylcarbazole),poly(thiophene), and other conductive polymers.

It is preferable to use in the light-emitting layer a material in whichcarriers transported and injected from the hole transport layer and theelectron transport layer are efficiently recombined to produce excitonsand are deactivated by radiation to emit light in a high emissionquantum yield. In general, a mixture of a host compound having carriertransport property and a guest compound having light-emitting propertyis more preferably used because light with high luminance can be emittedwith high emission efficiency.

A generally known fluorescent material or phosphorescent material may beused as the above-mentioned guest compound. The concentration of theguest compound with respect to the host compound is in the range of 0.01wt % to 50 wt % and preferably 1 wt % to 30 wt %. Further, multiplelight-emitting materials may be incorporated into the light-emittinglayer for the purposes of causing the light-emitting layer to emit lightbeams having multiple colors and of aiding transfer of excitons orcharges. The guest compound may be incorporated into the entirety of thelayer formed of the host compound uniformly or with a concentrationgradient, or may be partially incorporated into a specific region of thehost compound layer so that the layer has a region free of the guestcompound.

The material for the organic light-emitting device of the presentinvention may be used as a guest compound together with any other hostcompound.

Examples of such a material for the light-emitting layer as describedabove include, but are not limited to, the following compounds as wellas the azafluorene derivative as the material for the organiclight-emitting device of the present invention: a fused aromatic ringcompound (such as a fluorene derivative, a pyrene derivative, atetracene derivative, an anthracene derivative, a fluoranthenederivative, a benzofluoranthene derivative, or rubrene), a quinacridonederivative, a coumarin derivative, a stilbene derivative, an organicaluminum complex such as tris(8-quinolinolato)aluminum, an organicberyllium complex, a polymer derivative such as apoly(phenylenevinylene) derivative, a poly(fluorene) derivative or apoly(phenylene) derivative, and a phosphorescent metal complex (such asan iridium complex, a platinum complex, a rhenium complex, a coppercomplex, a europium complex or a ruthenium complex).

A material in which electrons are easily injected from the cathode andwhich has an electron transport property of transporting the injectedelectrons to the light-emitting layer, is preferably used in theelectron transport (injection) layer, and the material is selected inconsideration of, for example, a balance between the amount of holes tobe injected from the hole transport layer into the light-emitting layerand carrier mobility in the light-emitting layer. Examples of such anelectron injection/transport material include, but are not limited to,an oxadiazole derivative, an oxazole derivative, a pyrazine derivative,a triazole derivative, a triazine derivative, a quinoline derivative, aquinoxaline derivative, a phenanthroline derivative, a diazafluorenederivative, and an organic aluminum complex as well as the azafluorenederivative as the material for the organic light-emitting device of thepresent invention.

An anode material desirably has a work function as large as possible.Examples of the anode material include a metal such as gold, platinum,silver, copper, nickel, palladium, cobalt, selenium, vanadium, tungsten,and alloys thereof, and metal oxides such as tin oxide, zinc oxide,indium oxide, indium tin oxide (ITO) and indium zinc oxide may be used.Further, a conductive polymer such as polyaniline, polypyrrole, orpolythiophene may also be used. Each of these electrode substances maybe used alone, or two or more of them may be used in combination.Further, the anode may have a single layer structure or a multilayerstructure.

A cathode material preferably has a small work function, and includes:for example, alkali metals such as lithium; alkali earth metals such ascalcium: simple metals such as aluminum, titanium, manganese, silver,lead, or chromium; and alloys of plural metals, such as amagnesium-silver alloy, an aluminum-lithium alloy, or analuminum-magnesium alloy. A metal oxide such as indium tin oxide (ITO)may also be used. Each of these electrode materials may be used alone,or two or more of them may be used in combination. Further, the cathodemay have a single layer structure or a multilayer structure.

A substrate to be used in the organic light-emitting device of thepresent invention includes, but is not limited to, an opaque substratesuch as a metallic substrate or a ceramic substrate, and a transparentsubstrate made of glass, quartz or a plastic. In addition, a luminescentcolor can be controlled by using in the substrate a color filter film, afluorescent color conversion filter film, a dielectric reflective film,etc.

It should be noted that the produced organic light-emitting device maybe provided with a protective layer or a sealing layer for the purposeof preventing the device from coming into contact with, for example,oxygen or moisture. Examples of the protective layer include: aninorganic material film such as a diamond thin film, or a film formed ofa metal oxide or a metal nitride; a polymer film such as a polymer filmformed of a fluorine resin, polyethylene, a silicone resin, or apolystyrene resin; and a film formed from a photocurable resin. Inaddition, the device itself may be covered with, for example, glass, agas impermeable film or a metal, and packaged with an appropriatesealing resin.

A thin film transistor (TFT) may be produced on a substrate, and thenthe organic light-emitting device of the present invention may beproduced to be connected to TFT.

As for the emission direction of the device, it may have a bottomemission structure in which light is emitted from a substrate side, or atop emission structure in which light is emitted from the side oppositeto the substrate.

In the organic light-emitting device of the present invention, the layercontaining the material for the organic light-emitting device of thepresent invention and other layers formed from organic compounds areeach formed by the following method. A thin film is formed by a vacuumdeposition method, an ionized deposition method, sputtering, a plasmadeposition method, or a known coating method in which the compound isdissolved in an appropriate solvent. Examples of the coating method toform a thin film include a spin coating, dipping, casting, LB or inkjetmethod. In particular, when forming a film by a coating method, the filmmay be formed by using the compound in combination with an appropriatebinder resin.

Examples of the binder resin include, but are not limited to, apolyvinyl carbazole resin, a polycarbonate resin, a polyester resin; anABS resin, an acrylic resin, a polyimide resin, a phenol resin, an epoxyresin, a silicone resin and a urea resin. These binder resins may eachbe used alone, or two or more of them may be mixed and used as ahomopolymer or a copolymer. Further, an additive such as a knownplasticizer, antioxidant or ultraviolet absorber may be used incombination as required.

In particular, when an organic layer containing the azafluorenederivative as the material for the organic light-emitting device of thepresent invention is formed by, for example, a vacuum deposition methodor a solution coating method, the layer hardly undergoes crystallizationor the like, and is excellent in stability over time.

The layer containing the material for the organic light-emitting deviceof the present invention is formed into a thin film having a thicknessof less than 10 μm, preferably 0.5 μm or less, and more preferably 0.01to 0.5 μm.

Hereinafter, the present invention will be described specifically by wayof working examples. The present invention is by no means limited tothese working examples.

Example 1 Synthesis of Exemplified Compound 215

(1) Synthesis of Intermediate Compound M1

A solution of 68.3 g (381 mmol) of 1-azaphenanthrene and 157 g (470mmol) of iodopentoxide in acetic acid was stirred under heat at 108° C.for 2 hours. After the reaction liquid had been cooled to roomtemperature, water was added to the reaction liquid to crystallize theproduct, and then the crystals were filtered off. Subsequently, theresultant crystal was dissolved in chloroform, washed with an aqueoussolution of sodium hydrogen carbonate and an aqueous solution of sodiumthiosulfate, dried, and exsiccated by concentration, whereby 53.9 g of1-azaphenanthrene-5,6-dione were obtained (68% yield).

Subsequently, in a stream of argon, 1.5 L of a 10% aqueous solution ofsodium hydroxide was added to 51.0 g (244 mmol) of1-azaphenanthrene-5,6-dione, and heated and stirred at 85° C. for 90minutes. After the mixture was cooled to room temperature, theprecipitate was filtered out. The filtrate was extracted with chloroformand concentrated, and added to the precipitate, whereby a crude materialwas obtained. The crude material was purified by chromatography onsilica gel with toluene/ethyl acetate=10:1 to give 16.8 g of4-azafluorene-9-one (37.9% yield).

Subsequently, in a stream of argon, 500 mL of diethylene glycol wasadded to 16.8 g (92.6 mmol) of 4-azafluorene-9-one and 25 mL (370 mmol)of hydrazine monohydrate, and was heated and stirred at 168° C. for 3hours. After the reaction liquid was cooled to room temperature, anaqueous solution of sodium chloride was added to the reaction liquid,and then, was extracted with ethyl acetate. The organic phase was washedwith water, dried over sodium sulfate and concentrated, to therebyobtain 15.3 g of 4-azafluorene (99% yield).

Subsequently, in a stream of argon, 15.1 g (90.4 mmol) of 4-azafluorenewas dissolved in 100 mL of dehydrated THF, and 23.3 g (208 mmol) oftert-butoxypotassium was added to the solution at −11° C. understirring. After that, the mixture was stirred for 1 hour. Subsequently,15 mL (208 mmol) of iodomethane were added to the mixture. Thetemperature of the mixture was raised to room temperature, and themixture was stirred for 2 hours. After completion of the reaction, waterwas added to the mixture to terminate the reaction, extracted withtoluene, washed with an aqueous solution of sodium thiosulfate and asaturated salt solution, dried over sodium sulfate, and concentrated.The concentrate was purified by treatment with activated clay in atoluene solution, whereby 16.5 g of 9,9-dimethyl-4-azafluorene asIntermediate Compound M1 were obtained (94% yield).

(2) Synthesis of Intermediate Compound M2

In a stream of argon, 16.45 g (84.3 mmol) of Intermediate Compound M1was dissolved in 50 mL of chloroform, 30 g (101 mmol) ofmethachloroperbenzoic acid (MCPBA) was added to the solution at 25° C.with stirring, and stirred at room temperature for 2 hours. After thereaction, sodium thiosulfate was added to the mixture, and dried oversodium sulfate and filtrated. After that, the filtrate was concentratedand the slurry was washed with chloroform, whereby a crude material wasobtained. The crude material was purified by chromatography on silicagel with ethyl acetate:methanol=1:1 to give 17.2 g of an N-oxide ofIntermediate Compound M1 (97% yield).

Subsequently, 30 mL of phosphorus oxychloride was added to 17.1 g (81.0mmol) of the above N-oxide, and heated and stirred at 95° C. for 10hours. After the reaction, the reaction liquid was concentrated, andthen chloroform was added to the concentrate. The chloroform solutionwas added dropwise to a saturated aqueous solution of sodium hydrogencarbonate, and stirred for 1 hour. The mixture was extracted withchloroform, washed with a saturated salt solution, dried over sodiumsulfate, and concentrated, whereby a crude material was obtained.

The crude material was purified by chromatography on silica gel withchloroform to give 9.28 g of Intermediate Compound M2[3-chloro-9,9-dimethyl-4-azafluorene] (50% yield).

(3) Synthesis of Exemplified Compound 215

Under nitrogen, the following compounds were added to the mixed solventof toluene (30 mL) and ethanol (15 mL).

Intermediate Compound M2: 0.60 g (2.61 mmol)

Compound M3(2,7-bis(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9,9-dimethyl-9H-fluorene):0.53 g (1.19 mmol)

Tetrakis(triphenylphosphine)palladium: 0.14 g (0.12 mmol)

Further, 14 mL of a 10 wt % aqueous solution of sodium carbonate wereadded to the mixture, and heated and refluxed at 69° C. for 10 hoursunder stirring. After the reaction, the organic phase was extracted withtoluene, washed with water, dried over sodium sulfate, and concentrated,whereby a crude material was obtained. The crude material was purifiedby chromatography on silica gel with chloroform to give 329 mg ofExemplified Compound 215 (48% yield).

The M⁺ of the compound was identified as 580.3 by matrix-assisted laserdesorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS).Further, the structure of the compound was also identified by ¹H-NMRmeasurement. As a result, an NMR spectrum shown in FIG. 4 was obtained.

Further, each of the following exemplified compounds can be synthesizedby the same synthesis method as in Example 1-(3).

(Exemplified Compound 101): Exemplified Compound 101 can be obtained inthe same manner as in Example 1-(3) except that2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9,9-dimethyl-9H-fluoreneis used instead of Compound M3.

(Exemplified Compound 108): Exemplified Compound 108 can be obtained inthe same manner as in Example 1-(3) except that 3,5-diphenylboronic acidis used instead of Compound M3.

(Exemplified Compound 131): Exemplified Compound 131 can be obtained inthe same manner as in Example 1-(3) except that:6-bromo-3-chloro-9,9-dimethyl-4-azafluorene is used instead ofIntermediate Compound M2; and2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9,9-dimethyl-9H-fluoreneis used instead of Compound M3.

(Exemplified Compound 233): Exemplified Compound 233 can be obtained inthe same manner as in Example 1-(3) except that2,7-bis[4-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenyl]-9,9-dimethyl-9H-fluoreneis used instead of Compound M3.

(Exemplified Compound 234): Exemplified Compound 234 can be obtained inthe same manner as in Example 1-(3) except that2,7-bis[3-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)phenyl]-9,9-dimethyl-9H-fluoreneis used instead of Compound M3.

(Exemplified Compound 303): Exemplified Compound 303 can be obtained inthe same manner as in Example 1-(3) except that 3-quinoline boronic acidis used instead of Compound M3.

(Exemplified Compound 404): Exemplified Compound 404 can be obtained inthe same manner as in Example 1-(3) except that2,7-bis(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9,9-dimethyl-4,5-diazafluoreneis used instead of Compound M3.

(Exemplified Compound 501): Exemplified Compound 501 can be obtained inthe same manner as in Example 1-(3) except that 1,3,5-benzene triboronicacid is used instead of Compound M3.

(Exemplified Compound 604): Exemplified Compound 604 can be obtained inthe same manner as in Example 1-(3) except that6-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9,9-dimethyl-4-azafluoreneis used instead of Compound M3.

(Exemplified Compound 722): Exemplified Compound 722 can be obtained inthe same manner as in Example 1-(3) except that6-bromo-9,9-dimethyl-4-azafluorene is used instead of IntermediateCompound M2.

(Exemplified Compound 907): Exemplified Compound 907 can be obtained inthe same manner as in Example 1-(3) except that2-chloro-9,9-dimethyl-1-azafluorene is used instead of IntermediateCompound M2.

(Exemplified Compound 615): Exemplified Compound 615 can be obtained inthe same manner as in Example 1-(3) except that6-bromo-3-chloro-9,9-dimethyl-4-azafluorene is used instead ofIntermediate Compound M2; and6-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9,9-dimethyl-4-azafluoreneis used instead of Intermediate Compound M3.

(Exemplified Compound 707): Exemplified Compound 707 can be obtained inthe same manner as in Example 1-(3) except that2,6-dibromo-9,9-dimethyl-4-azafluorene is used instead of IntermediateCompound M2; and2-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9,9-dimethyl-9H-fluoreneis used instead of Compound M3 in Example 1-(3).

(Exemplified Compound 812): Exemplified Compound 812 can be obtained inthe same manner as in Example 1-(3) except that:2,7-dibromo-9,9-dimethyl-4,5-diazafluorene is used instead ofIntermediate Compound M2; and6-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9,9-dimethyl-4-azafluoreneis used instead of Compound M3.

(Exemplified Compound 814): Exemplified Compound 814 can be obtained inthe same manner as in Example 1-(3) except that:2,7-dichloro-1,8-naphthyridin is used instead of Intermediate CompoundM2; and6-(4,4,5,5-tetramethyl[1,3,2]dioxaborolan-2-yl)-9,9-dimethyl-4-azafluoreneis used instead of Compound M3.

Example 2 Synthesis of Exemplified Compound 232

In the same manner as in Example 1-(3), under nitrogen, the followingcompounds were heated and refluxed in a mixed solvent of toluene (25mL), ethanol (12 mL) and a 10 wt % aqueous solution of sodium carbonate(12 mL) at 68° C. for 6 hours under stirring. Intermediate Compound M2:0.57 g (2.48 mmol)3,6-bis(4,4,5,5-tetramethyl[1,3,2]dioxaborolane-2-yl)-9,9-dimethyl-9H-fluorene):0.50 g (1.12 mmol) Tetrakis(triphenylphosphine)palladium: 0.13 g (0.12mmol)

After the reaction, the organic phase was extracted with toluene, washedwith water, dried over sodium sulfate, and concentrated, whereby a crudematerial was obtained. The crude material was purified by chromatographyon silica gel with toluene/chloroform=1:3 to give 422 mg of ExemplifiedCompound 215 (65% yield).

The of the compound was identified as 580.3 by matrix-assisted laserdesorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS).

Example 3

An organic light-emitting device having a structure shown in FIG. 3 wasproduced by the following method.

Indium tin oxide (ITO) was formed into a film having a thickness of 120nm by a sputtering method on a glass substrate (the substrate 1) so asto serve as the anode 2, and the resultant was used as a transparentconductive supporting substrate. An organic layer and a layercorresponding to a cathode were successively formed on the transparentconductive supporting substrate by vacuum deposition with resistanceheating in a vacuum chamber having a pressure of 10⁻⁴ Pa. To bespecific, Compound A shown in the following formula was first formedinto a film having a thickness of 20 nm so as to serve as the holetransport layer 5. Compound B shown in the following formula was thenformed into a film having a thickness of 30 nm so as to serve as thelight-emitting layer 3. Next, Exemplified Compound 215 was formed into afilm having a thickness of 20 nm so as to serve as the electrontransport layer 6. Subsequently, KF was formed into a film having athickness of 1 nm. Finally, Al was formed into a film having a thicknessof 120 nm. The KF film and the Al film each function as the cathode 4.

The resultant organic light-emitting device was covered with aprotective glass plate in a dry air atmosphere lest the device shoulddegrade owing to the adsorption of moisture, and was sealed with anacrylic resin-based adhesive.

A DC voltage was applied to the device thus obtained while the ITOelectrode (the anode 2) was defined as a positive electrode and the Alelectrode (the cathode 4) was defined as a negative electrode. As aresult, the device was observed to emit blue light at a low voltage, andshowed a small reduction in luminance even after energization for 100hours.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-349580, filed Dec. 26, 2006, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An organic light-emitting device comprising: apair of electrodes composed of an anode and a cathode, either the anodeor the cathode being a transparent or semi-transparent electrode, and anorganic compound layer interposed between the pair of electrodes,wherein the organic compound layer contains an azafluorene derivativerepresented by following general formula (III):

wherein m represents an integer of 2 to 4, a represents an integer of 0to 4, and b represents an integer of 0 to 2; wherein X₁ and X₂ eachindependently represent a substituent selected from the group consistingof a substituted or unsubstituted alkyl group, a substituted orunsubstituted alkoxy group, a substituted or unsubstituted aromatichydrocarbon group, a substituted or unsubstituted heterocyclic group,and a substituted amino group; wherein Ar represents an m-valentaromatic hydrocarbon group which may be substituted; and wherein R₁ andR₂ each independently represent an alkyl group which is unsubstituted ormay be substituted by a fluorine atom.
 2. The organic light-emittingdevice according to claim 1, wherein the organic compound layer is anelectron transport layer.
 3. An organic light-emitting devicecomprising: a pair of electrodes composed of an anode and a cathode,either the anode or the cathode being a transparent or semi-transparentelectrode, and an organic compound layer interposed between the pair ofelectrodes, wherein the organic compound layer contains an azafluorenederivative represented by following general (IV):

wherein a represents an integer of 0 to 4, and b represents an integerof 0 to 2; wherein X₁ and X₂ each independently represent a substituentselected from the group consisting of a substituted or unsubstitutedalkyl group, a substituted or unsubstituted alkoxy group, a substitutedor unsubstituted aromatic hydrocarbon group, a substituted orunsubstituted heterocyclic group, and a substituted amino group; whereinAr represents a polycyclic aromatic hydrocarbon group which may besubstituted; and wherein R₁ and R₂ each independently represent an alkylgroup which is unsubstituted or may be substituted by a fluorine atom.4. The organic light-emitting device according to claim 3, wherein theorganic compound layer is an electron transport layer.
 5. The organiclight-emitting device according to claim 1, further comprising a colorfilter and a TFT.
 6. The organic light-emitting device according toclaim 3, further comprising a color filter and a TFT.